1. Field of the Invention
The present invention relates to a sealing system for heavy lids for pits used in servicing aircraft at docking, loading and fueling terminals.
2. Description of the Prior Art
At modern aircraft terminals servicing of aircraft on the ground is frequently performed using prefabricated pits which are installed at aircraft docking, fueling and loading areas beneath the surface of the tarmac across which aircraft travel during docking and departure maneuvers. The pits are typically formed of fiberglass, steel or aluminum and are constructed as enclosures with surrounding walls, and an access lid seated in an opening at the top of the walls. The pits are installed below the surfaces of loading and refueling aprons at aircraft terminals, remote parking locations and at maintenance bases.
The purpose of the pits is to allow ground support functions to be carried out from subsurface enclosures. These ground support functions include the provision of fuel, the provision of electricity to the aircraft while it is in the docking area, the provision of air for cooling the aircraft interior, the provision of pressurized air for starting the aircraft engines, and for other aircraft support activities on-the ground. The use of subsurface pits eliminates the need for mobile trucks, carts and other vehicles which are otherwise present in the loading area and which interfere with the arrival and departure of aircraft in the vicinity of a loading gate. The use of subsurface pits also allows the provision of fuel, power, cooling and pressurized air, and other supplies from a central location. The necessary fluid supplies and electrical power can be generated or stored with a greater efficiency at a central location, as contrasted with mobile generating or supply vehicles.
The pits located below the aircraft terminal area house valves, junction boxes, cooling air terminations and other terminal equipment that is temporarily connected to an aircraft that has been docked. Umbilical pipes and lines, otherwise housed within the pits, are withdrawn from the pits through hatches therein and are coupled to a docked aircraft to supply it with fuel, air for cooling the aircraft interior, pressurized air for starting the engines, and electrical power.
The pits are constructed with either hinged or totally removable lids that can be moved between open positions allowing access to the pits and closed positions which are flush with the surfaces of the docking, loading or refueling areas across which aircraft travel and beneath which the pits are mounted. Because the pits are located below grade, there is a tendency for water, spilled fuel, dust and debris to fall into the pits through the interstitial cracks surrounding the pit lids within the frames in which the Pits are mounted. Since these vertical interstitial gaps represent a point below grade, rainwater and melting snow carries both liquid and solid debris into the gaps surrounding the pit lids. The liquid flows down into the pits carrying some of the debris with it. Also, whenever a pit lid is opened any debris remaining on the shoulder supporting the lid frame is likely to fall into the pit as well.
The entry of dirt, debris and unwanted liquid into the pit enclosure can create problems. Such contaminants accelerate rusting and contribute to jamming of mechanical mechanisms, such as valves and latches. Also, dirt and debris tend to obscure the visibility of dials on pressure and volume gauges, and on dials indicating voltage levels. and other readings.
To prevent unwanted contaminants from entering a subsurface pit through the interstitial gaps between the pit lid and the surrounding frame, various sealing systems have been employed. Such conventional sealing systems employ "wiper" seals in which a peripheral seal around a pit lid drags against the surrounding lid mounting frame wall as the lid is seated and unseated relative to the mounting frame. The effect of friction against the mounting frame wall rapidly degrades the integrity of the seal and significantly detracts from the effectiveness of the seal in a relatively short period of time. Thus, conventional pit lid sealing systems have proven unsatisfactory.
Another problem with conventional pit lid sealing systems is that when the seals do degrade they are difficult to replace. Conventional seals are formed of an elastomeric material secured by an adhesive to the edge of the pit lids. When conventional seals become worn and start to leak, they must be pulled away from the lid and the old adhesive must be removed from the edge of the lid before a new replacement seal can be installed. The removal of the old adhesive is a time consuming process, so that worn and deteriorated seals are often not replaced as frequently as they should be.